Production of kerosene jet fuels

ABSTRACT

A process for the production of kerosene jet fuels in which kerosene boiling range petroleum fractions are contacted with hydrogen and a catalyst comprising a noble metal and fluoride on alumina, the process being further characterized by control of the kerosene feed water content to a low level (e.g., 10 p.p.m. or lower).

United States Patent inventors Robert E. Robinson;

Apr. 7, 1969 Sept. 2], 1971 Shell Oil New York, N.Y.

App]. No. Filed Patented Assignee PRODUCTION OF KEROSENE JET FUELS 9 Claims, No Drawings US. Cl 208/112, 208/57, 208/89, 208/145, 208/177, 208/187,

Int. Cl ..C 10g 13/02, C07e 5/16, BOlj 11/08 Field of Search 208/15,

William K. Meerbott, both of Houston, Tex.

References Cited Primary ExaminerDelbert E. Gantz Assistant Examiner-G. E. Schmitkons Attorney-Harold L. Denkler ABSTRACT: A process for the production of kerosene jet fuels in which kerosene boiling range petroleum fractions are contacted with hydrogen and a catalyst comprising a noble metal and fluoride on alumina, the process being further characterized by control of the kerosene feed water content to a low level (e.g., l0 p.p.m. or lower).

PRODUCTION OF KEROSENE JET FUELS DISCUSSION OF THE PRIOR ART ln recent years aviation turbine fuels have become a major petroleum product. Acceptable kerosene-type turbine fuels must meet certain specifications which are seldom found in naturally occurring petroleum distillates. In general, such a kerosene fuel must have the following specifications:

APl Gravity-39-51 Smoke PointGreater than 20 Luminometer No.Greater than 45 Aromatic Content-Less than 20 percent.

These fuels have a boiling range from about 300 to 600 F. and must have a reasonable distribution of fractions throughout the boiling range (limits on the distribution are also fixed by specification).

Very few natural distillates possess the necessary combined properties. Consequently, these fuels must be synthetically produced and the various hydrocarbon types (paraffins, naphthenes and aromatics) carefully balanced in the composition to produce the desired properties.

Paraffins, including isoparaffins, have a relatively high smoke point and gravity which makes them desirable components. However, they have relatively low heating value (B.t.u./lb.). Moreover, most natural kerosene boiling range fractions contain substantial amounts of aromatics and naphthene compounds making the production of entirely paraffinic fuels economically unattractive.

Aromatics, on the other end of the scale, have low smoke point and API gravity properties but high heating value.

Naphthenes fall in between. They have relatively high heating value and relatively poor smoke point and gravity properties.

Thus, feasible jet fuels must be a balanced composition containing at least paraffins and naphthenes. Aromatics may or may not be included depending on the quality of the other components.

Polynaphthene compounds are also usually present in the kerosene distillates and are much like aromatics, i.e., have poor gravity and smoke point characteristics.

Numerous proposals have been made in the literature for achieving acceptable jet fuels. For example, various processes which depend on the removal of aromatics by separation or hydrogenation have been described.

We have discovered a new process for the efficient production of jet fuels of specification quality from hydrocarbon distillates which contain substantial amounts of ring structures (aromatics and naphthenes).

The process involves simultaneous aromatic hydrogenation and ring opening in a single reaction zone.

SUMMARY OF THE INVENTION ln broad aspect the present invention is a process for the hydrogenation/ring opening of kerosene boiling range hydrocarbon fractions, having substantial amounts of cyclic compounds, characterized by contacting a kerosene fraction in the presence of hydrogen with a catalyst comprising at least 1 w/o platinum group metal and 0.5 w/o fluoride on alumina, the process being further characterized by maintaining the kerosene feed water content to below about ppm. by weight.

Kerosene boiling range fractions suitable for the process of the present invention may be derived from a variety of sources. In general, fractions in the boiling range from about 300 to 600 C. are suitable. Examples of suitable feeds are, for example, straight run, catalytically cracked, or hydrocracked fractions and combinations thereof. The fractions for which the present process is advantageous have APl gravities lower than 39 and smoke points which are usually below about 20. Such fractions contain substantial amounts of aromatic and naphthenic ring compounds, i.e., a suitable straight run fraction from a naphthenic crude which may con tain on the order of 10 to percent aromatics and 40 to 70 percent naphthenes. Hydrocracked kerosene fractions usually have higher aromatics content in the range of 30 to 60 percent.

When the kerosene feed contains relatively high contents of heteroatomic impurities such as nitrogen, sulfur or metallic compounds, hydrotreating to reduce or remove these impurities is desirable. Sulfur compounds are especially undesirable since they tend to poison the platinum group metal in the hydrogenation ring opening catalyst.

Hydrofining processes and catalysts suitable for use in connection with the present process are well known. Such catalysts generally comprise one or more of the various Group Group V] and Group VIII metals as well as the oxides and sulfides thereof supported on a porous carrier. Thus nickel molybdenum sulfide on alumina is an example of a useful, commercially available catalyst.

Hydrofining can be carried out over a wide range of conditions that depend upon the particular hydrocarbon feed and catalyst used. Temperatures in the range of 625 to 750 F., pressures in the range of 400 to 1,500 p.s.i.g., liquid hourly space velocities of about 0.5 to 5 and hydrogen to oil ratios of about 500 to 10,000 standard cubic feet of H per barrel of feed are customary conditions. Partial hydrogenation of aromatics in the kerosene boiling range may be effected in the hydrotreating reaction but is neither required for nor forms a part of the present invention.

The present process uses a catalyst composite which has certain critical concentrations of components. The predominant portion of the catalyst is a porous alumina support. Suitable alumina supports include activated alumina, gamma alumina, eta alumina, pseudo-alumina and the like. The catalyst contains at least 1 w/o of a platinum group metal and preferably about 1.5 w/o platinum.

The catalyst must also contain at least 0.5 w/o fluorine and preferably about 1 percent weight fluorine.

One of the surprising discoveries in development of the present process was the necessity for the addition of fluorine. Fluorine is customarily added to such catalyst composites to promote acid catalyzed reactions. The desired hydrogenation/ring opening reactions of the present invention are known to be metal catalyzed. Thus, the addition of a halogen would not be expected to aid in these reactions but instead to lead to undesirable hydrocracking.

While not wishing to be bound by the theory it is believed that the function of the fluorine is to aid in the conversion of six member ring structures to isomeric five member ring structures, which are more easily ring-opened by the hydrogenation metal. This theory will be further demonstrated in the examples included herein.

Platinum metal and fluorine may be added to the alumina support by various means known to the art. A convenient method involves competitive ion exchange of discrete particles (spheres, extrudates, etc.) of alumina with an aqueous solution of chloroplatinate ions and ammonium ions such as a dilute solution of chloroplatinic acid and ammonium mitrate. Nitrate and chloride ions are removed by washing and the composite is impregnated with a suitable fluoride compound such as a solution of ammonium bifluoride. Calcination decomposes the ammonium ion.

Competitive ion exchange results in highly dispersed platinum metal. This dispersion is preserved by careful reduction with a hydrogen-containing gas in a substantially moisture-free atmosphere.

The process may be carried out in any suitable equipment but preferably in a fixed bed reaction system where the catalyst is disposed as discrete particles in a reaction zone and the hydrocarbon feed passed therethrough in upward, downward or radial flow.

Reaction conditions for the present invention depend upon the kerosene feed composition properties and the catalyst composition and degree of activation.

Suitable conditions are temperatures in the range of 500 to 800 F., pressure in the range of 500 to 1,500 p.s.i.g., liquid hourly space velocities of from 0.5 to 5 volumes of feed per volume of catalyst per hour and hydrogen to hydrocarbon mole ratios of about 5 to 20.

The moisture content of the kerosene feed is especially important and should be maintained below about p.p.m. by weight and preferably at about 2 p.p.m. by weight. The importance of low water content will be demonstrated in the examples.

The following examples serve to further elucidate the practice and advantages ofthe present invention.

EXAMPLE 1 Catalysts were prepared with platinum contents of0.1, 0.68 and 1.5 w/o and 0.6 w/o fluorine by uniformly dispersing platinum on porous alumina. The metal was incorporated by competitive ion exchange of chloroplatinate ions in dilute ammonium nitrate solution. Fluorine was incorporated by impregnation of the catalyst with ammonium bifluoride solution. The catalysts were washed free of unreacted ions, dried, calcined and reduced in dry hydrogen. These catalysts were tested with a hydrotreated naphthenic kerosene fraction (310 to 540 F. boiling range) at 665 F., 1.5 liquid hourly space velocity (LHSV) and 10 H jhydrocarbon mole ratio. The results are shown in table 1.

TABLE 1 Pt/AlzOa-F Catalyst Feed 0. 1% 0.68% 1. 5%

Catalyst age, hours 144 3241 99 Conditions:

Temperature, F 665 665 665 Pressure, p.s.i.g.. 1, 600 1, 500 1, 500 LHSV 1. 5 1. 5 1. 6 Hg/Oll, molar 10 10 10 Yields:

C -C5, percent w 0.8 1. 5 1. 6 113-310 F., percent v 0. 8 6.7 7. 8 310 F.+, percent v 100.1 95.0 94. 7 Kerosene properties:

Gravity, API at 60 F 37.0 38. 5 40.3 40. 8 Hydrocarbon type, percent v:

Paraffins 20. 3 21. 4 25.1 27. 3 Naphthenes- 68. 7 77. 3 73. 7 71. 9 Aromatics 12. 0 1. 3 1. 2 0. 8 N aphthenes, total product (moles/100 g. of feed):

One-ring 0. 1782 0. 1921 0. 2320 Two-ring 0. 1844 0. 1584 0. 1435 Three-ring 0. 0593 0. 0454 0. 0172 Net decrease in rings, percent In 9. 9 14. 3

These results show that ring opening is greatest with the highest platinum-content catalyst. The results with the 0.1 We platinum catalyst are substantially the same as would be obtained by hydrogenation alone without ring-opening. Note that the paraffin content of the product is not greatly increased over that of the feed, the net effect being conversion of aromatics to naphthenes. This product does not meet the 39 APl minimum gravity specification. In all cases diand triring naphthenes are ring opened selectively with a net increase in monoring naphthenes and paraffins.

EXAMPLE 2 A catalyst prepared by competitive ion exchange of platinum and impregnation with fluoride of a commercial catalytic reforming catalyst was used to study the effect of moisture in the process. Platinum and fluoride were added as described in example 1 to give a catalyst having 1.5 w/o' platinum and 1 w/o fluorine. Prior to use the catalyst was calcined in a reactor with dry air, purged with nitrogen and reduced with dry hydrogen for 1 hour at atmospheric pressure.

The catalyst was used for ring opening a kerosene fraction like that in example 1. Conditions were 850 p.s.i.g., 660 F., 2 LHSV and 10 H joil ratio (mole). The kerosene was dried to a water level of 10 p.p.m. by weight by passing it over molecular sieves. After hours of processing the product AP] gravity was about 39.7. After 200 hours of operation of feed water level was increased to 570 p.p.m. and the product APl gravity immediately fell to 38.8. On returning to 10 p.p.m. water the product API gravity increased to 39.5.

During the dry operation the aromatics content of the product was about 3 percent (compared to 13 percent in the feed).

Thus, the effect of water in the system is to severely reduce ring openinggiving results much like simple hydrogenation of aromatics.

EXAMPLE 3 A catalyst substantially the same as the 1.5 w/o platinum catalyst described in example 2 was used for ring opening the 310-540 F. kerosene fraction of example 1 at 850 p.s.i.g., 660 F., 2 LHSV and 10 H loil ratio (mole). The kerosene was dried to 2 p.p.m. by weight water with molecular sieves. During 1,000 hours of operation (after which the run was terminated without evidence of catalyst deactivation) the product API gravity was 40 or above. Yield of product during this time was about 96 percent volume of 310 F. plus kerosene.

This operation under very dry conditions results in sufficient ring opening to provide a balanced specification jet fuel and significantly increases the long term process stability.

We claim as our invention:

1. A process for hydrogenating/ring-opening a feed consisting essentially of kerosene boiling range hydrocarbons wherein the feed substantially free of heteroatomic impurities is contacted in the presence of hydrogen with a catalyst comprising at least about 1.0 w/o of a platinum group metal and at least 0.5 w/o by weight fluorine on an alumina support at temperature in the range of about 500 to 800 F., a pressure in the range of about 500 to 1,500 p.s.i.g. and a hydrogen to hydrocarbon mole ratio of from about 5 to 20 and wherein the water content of the contacted hydrocarbons is below about 10 p.p.m. by weight.

2. The process of claim 1 wherein the water content of the contacted hydrocarbons is about 2 p.p.m. by weight.

3. The process of claim 1 wherein the contacted hydrocarbons are substantially free of sulfur compounds.

4. The process of claim 1 wherein the contacted hydrocarbons have a total ring content, aromatic plus napthenes, of greater than about 50 percent.

5. The process of claim 4 wherein the contacted hydrocarbons have a water content of about 2 p.p.m. by weight.

6. The process of claim 5 wherein the heteroatomic impurities have been removed by hydrotreating the kerosene boiling range hydrocarbons.

7. The process of claim 5 wherein the catalyst comprises about 1.5 w/o platinum and about 1 W10 fluorine on the alumina support.

8. The process of claim 1 wherein the kerosene boiling range hydrocarbons have an APl gravity of below about 39.

9. The process of claim 1 wherein the platinum group metal is platinum. 

2. The process of claim 1 wherein the water content of the contacted hydrocarbons is about 2 p.p.m. by weight.
 3. The process of claim 1 wherein the contacted hydrocarbons are substantially free of sulfur compounds.
 4. The process of claim 1 wherein the contacted hydrocarbons have a total ring content, aromatic plus napthenes, of greater than about 50 percent.
 5. The process of claim 4 wherein the contacted hydrocarbons have a water content of about 2 p.p.m. by weight.
 6. The process of claim 5 wherein the heteroatomic impurities have been removed by hydrotreating the kerosene boiling range hydrocarbons.
 7. The process of claim 5 wherein the catalyst comprises about 1.5 w/o platinum and about 1 w/o fluorine on the alumina support.
 8. The process of claim 1 wherein the kerosene boiling range hydrocarbons have an API gravity of below about
 39. 9. The process of claim 1 wherein the platinum group metal is platinum. 